JP7291056B2 - Wafer polishing method - Google Patents

Description

The present invention relates to a method of polishing a workpiece such as a semiconductor wafer.

For example, as disclosed in Patent Document 1, a polishing apparatus that polishes a wafer held on a chuck table with a polishing pad while supplying slurry to the wafer is a wafer having a preset thickness that is held on the chuck table and polished. A pad is pressed against the wafer for polishing.

That is, the polishing pad is lowered at high speed to a height position slightly higher than the set thickness of the wafer, and the load that can be measured when the polishing pad is pressed against the wafer from that height position can be detected, for example, 5 μm. The polishing pad is lowered (air-cut descent) at a slow speed of /second, and then the polishing pad is pressed against the wafer with a predetermined load to polish the upper surface of the wafer, which is the surface to be polished.

JP 2016-215284 A

In the polishing apparatus as described above, a wafer cassette storing a plurality of wafers in a shelf shape is unloaded one by one by a robot, held on a chuck table, and polished by a polishing pad. A plurality of wafers accommodated in this wafer cassette have a thickness difference of, for example, 100 μm to 200 μm. There is a demand to polish the plurality of wafers with the same polishing removal amount, that is, while applying the same polishing load.

However, if there is variation in the thickness of the wafer input, i.e., if a wafer thicker than the set thickness is held on the chuck table, the height position slightly above the set wafer thickness ( When the polishing pad is lowered at high speed to the polishing start position), the polishing pad comes into contact with a thick wafer, so the lower surface of the polishing pad strongly pushes the upper surface of the wafer, and a load larger than the allowable value is applied to the wafer. There is a problem of breaking the wafer.
Further, when a wafer thinner than the set thickness of the wafer is held on the chuck table, after the polishing pad is lowered at a high speed to a height position slightly above the set thickness of the wafer, for example, 5 μm/sec. Since the polishing pad is lowered by a longer distance than expected at such a slow speed, it takes a long time to bring the lower surface of the polishing pad into contact with the upper surface of the wafer.

Therefore, when polishing wafers using a polishing apparatus, even if the thickness of the plurality of wafers stored in the wafer cassette is not uniform, the wafers thicker than the wafer thickness set in the polishing apparatus and the set wafer thickness A wafer thinner than the wafer thickness can be polished in the same way as a wafer with a set thickness, that is, while applying a load within the same polishing load range, and the wafer is damaged and the lower surface of the polishing pad is damaged. There is a problem of preventing the time until contact with the upper surface from becoming longer.

In order to solve the above problems, the present invention comprises holding means for holding a wafer on a holding surface, polishing means for polishing the wafer by bringing the lower surface of the polishing pad into contact with the upper surface of the wafer held by the holding means, and the polishing. Wafer using a polishing apparatus comprising vertical movement means for moving the means in the vertical direction perpendicular to the holding surface, and a load sensor for measuring the load of pressing the polishing pad against the wafer held on the holding surface. a polishing method comprising: a preparation position positioning step of positioning the polishing pad at a preparation position in which a gap is provided between the upper surface of the wafer held by the holding surface and the lower surface of the polishing pad; After positioning the polishing pad, a lowering step of lowering and stopping the polishing pad at a preset distance and speed using the vertical movement means, and after the polishing pad is stopped by the lowering step, the load is applied. a determining step of determining whether or not the load value measured by the sensor is equal to or greater than a preset threshold; the descending step until the determining step determines that the load value measured by the load sensor is equal to or greater than the threshold; a repeating step of repeating the determining step; and when it is determined by the determining step that the load value measured by the load sensor is equal to or greater than the threshold value, a load within a predetermined load range including the threshold value is applied to the wafer. and a polishing step of polishing the wafer.

A wafer polishing method according to the present invention comprises a preparation position positioning step of positioning the polishing pad at a preparation position with a gap between the upper surface of the wafer held by the holding surface and the lower surface of the polishing pad; After positioning, the lowering step of lowering and stopping the polishing pad at a preset distance and speed using the vertical movement means, and after stopping the polishing pad by the lowering step, the load value measured by the load sensor is a determination step of determining whether or not the load value measured by the load sensor is equal to or greater than a preset threshold; a repeating step of repeating the descending step and the determination step until the determination step determines that the load value measured by the load sensor is equal to or greater than the threshold; a polishing step of polishing the wafer while applying a load within a predetermined load range including the threshold value to the wafer when it is determined that the load value measured by the load sensor is equal to or greater than the threshold value by Even if the thickness of a plurality of wafers is not uniform, wafers thicker than the thickness set in the polishing apparatus and wafers thinner than the set thickness are polished in the same way as wafers with the set thickness. It is possible to polish the wafer while applying a polishing load of 100% to the wafer, and it is possible to prevent damage to the wafer due to contact with the polishing pad and a longer time until the lower surface of the polishing pad comes into contact with the upper surface of the wafer. becomes.

It is a perspective view which shows an example of a polishing apparatus. 4 is a cross-sectional view showing an example of the structure of polishing means and holding means; FIG. 5 is a graph showing the height position of a polishing pad and a graph showing load values measured by a holder load sensor when thin wafers are polished by the wafer polishing method according to the present invention. 7 is a graph showing the height position of a polishing pad and a graph showing load values measured by a holder load sensor when a wafer thinner than a set thickness is polished by a conventional wafer polishing method. 7 is a graph showing the height position of a polishing pad and a graph showing load values measured by a holder load sensor when a wafer having a set thickness is polished by a conventional wafer polishing method; 5 is a graph showing the height position of the polishing pad and the load value measured by the holder load sensor when a thick wafer is polished by the wafer polishing method according to the present invention. 7 is a graph showing the height position of a polishing pad and a graph showing load values measured by a holder load sensor when a wafer thicker than a set thickness is polished by a conventional wafer polishing method.

The polishing apparatus 1 shown in FIG. 1 polishes a wafer W held on a holding surface 300a of a holding means 30 on a spindle 70 having an axis in a vertical direction (Z-axis direction) perpendicular to the holding surface 300a. It is an apparatus for polishing with a pad 76, and includes an apparatus base 10 extending in the Y-axis direction and a column 11 standing on the apparatus base 10 on the rear side (-X direction side).

The wafer W shown in FIG. 1 is, for example, a laminated wafer in which a plurality of circular semiconductor wafers made of silicon or the like are laminated, and the upper surface Wb facing upward in FIG. 1 is the surface to be polished. The lower surface Wa of the wafer W facing downward in FIG. 1 is protected by, for example, a protective tape (not shown) adhered thereto. In addition, the wafer W is not limited to the example of this embodiment.

The polishing apparatus 1 has a cassette mounting table (not shown) on which the wafer cassette 21 shown in FIG. 1 can be mounted. It is

The wafer cassette 21 has, for example, a bottom plate 210, a top plate 211, a rear wall 212, two side walls 213, and an opening 214 on the front side (+X direction side). can be carried in and out. Inside the wafer cassette 21, a plurality of shelves 215 are formed at predetermined intervals in the vertical direction, and the wafers W can be accommodated one by one on the shelves 215. As shown in FIG. The configuration of the wafer cassette 21 is not limited to this example.
For example, the wafers W stored in the wafer cassette 21 have a thickness difference of about 100 μm to about 200 μm depending on the number of laminated semiconductor wafers, and the operator knows this fact.

The holding means 30 having a circular outer shape is, for example, a chuck table, and includes a suction portion 300 made of a porous member or the like for sucking the wafer W, and a frame 301 supporting the suction portion 300 . The suction unit 300 communicates with a suction source (not shown) such as a vacuum generator, and the suction force generated by the suction source is transmitted to the holding surface 300a, which is the upper surface (exposed surface) of the suction unit 300. Thus, the holding means 30 can hold the wafer W by suction on the holding surface 300a.
The holding means 30 is surrounded by a cover 39 and is rotatable about the Z-axis by a rotating means (not shown) arranged below the holding means 30 .

Below the holding means 30, the cover 39, and the bellows cover 39a connected to the cover 39, Y-axis moving means 34 for horizontally moving the holding means 30 and the cover 39 in the Y-axis direction is provided. The bellows cover 39a expands and contracts in the Y-axis direction as the holding means 30 and the cover 39 move.

The Y-axis moving means 34 includes a ball screw 340 having an axial center in the Y-axis direction, a pair of guide rails 341 arranged parallel to the ball screw 340, a motor 342 connected to the ball screw 340 and rotating the ball screw 340, A movable plate 343 is provided with an internal nut screwed onto the ball screw 340 and having a bottom portion in sliding contact with the guide rail 341 . The holding means 30 arranged on the movable plate 343 reciprocates in the Y-axis direction.

As shown in FIG. 2, for example, on the movable plate 343, an inclination adjusting means 36 for adjusting the inclination of the holding surface 300a of the holding means 30 is arranged. For example, two or more tilt adjusting means 36 are provided on the upper surface of the movable plate 343 at regular intervals in the circumferential direction. That is, for example, two tilt adjusting means 36 and a support column (not shown) are arranged at intervals of 120 degrees in the circumferential direction of the holding means 30 . The two tilt adjusting means 36 are, for example, an electric cylinder or an air cylinder in which the rod 360 can move up and down in the Z-axis direction from inside the cylinder 361, but are not limited thereto. It may be composed of an element or the like. By vertically moving the rods 360 of the two tilt adjusting means 36, the tilt of the holding surface 300a can be adjusted.

The holding means 30 can be tilted by the tilt adjusting means 36 while being fixed on the table base 33 .
The table base 33 to which the tilt adjusting means 36 is connected to the lower surface is composed of, for example, two circular plate-shaped base plates 331 and 332 in plan view. The two base plates 331 and 332 are integrated by fixing bolts 333, and sandwich, for example, three table load sensors 38 (only two are shown in FIG. 2) from above and below. there is

Three table load sensors 38 for measuring the load of pressing the polishing pad 76 against the wafer W held on the holding surface 300a of the holding means 30 shown in FIGS. That is, they are located at the vertices of an equilateral triangle, and are screwed between the base plate 331 and the base plate 332 by fixing bolts 333 . Therefore, the table load sensor 38 supports the holding means 30 and receives and detects a load applied to the holding means 30 from the +Z direction. The table load sensor 38 is composed of, for example, a dynamometer manufactured by Kistler using a piezoelectric element.

As shown in FIG. 1, on the front surface of the column 11, a vertically moving means 5 for moving the polishing means 7 in the vertical direction perpendicular to the holding surface 300a of the holding means 30 is arranged. The vertical movement means 5 includes a ball screw 50 extending in the Z-axis direction, a pair of guide rails 51 arranged parallel to the ball screw 50, a motor 52 connected to the upper end of the ball screw 50 and rotating the ball screw 50, It is provided with an elevating plate 53 having an internal nut screwed onto the ball screw 50 and a side portion of which is in sliding contact with the guide rail 51 . Guided and reciprocated in the Z-axis direction, the polishing means 7 fixed to the lifting plate 53 is fed in the Z-axis direction for polishing.

As shown in FIG. 1, the polishing means 7 includes a spindle 70 whose axial direction is the Z-axis direction, a housing 71 that rotatably supports the spindle 70, a motor 72 that rotationally drives the spindle 70, and a lower end of the spindle 70. , a circular plate-shaped platen 74 attached to the lower surface of the mount 73, a polishing pad 76 attached to the lower surface of the platen 74, and a housing 71 supported by the vertical movement means 5 and a holder 75 whose side surface is fixed to the elevating plate 53 .

The circular polishing pad 76 in plan view is made of, for example, non-woven fabric such as felt, and has a size approximately equal to the diameter of the platen 74 and a diameter larger than the diameter of the wafer W held by the holding means 30 . It's becoming

For example, as shown in FIG. 2, between the bottom plate 75b and the side plate 75c of the holder 75, a holder load sensor for measuring the load of pressing the polishing pad 76 against the wafer W held on the holding surface 300a of the holding means 30 is provided. 77 are arranged so as to be sandwiched from above and below. Three (only two are shown in FIG. 2) holder load sensors 77 are positioned at intervals of 120 degrees in the circumferential direction of the polishing pad 76, that is, at the vertices of an equilateral triangle. , are screwed between the bottom plate 75b of the holder 75 and the side plate 75c. The holder load sensor 77 is composed of, for example, a dynamometer manufactured by Kistler using a piezoelectric element.
Note that the polishing apparatus 1 may include at least one of the holder load sensor 77 and the table load sensor 38 .

A polishing liquid flow path (not shown) extending in the Z-axis direction is formed from the inside of the spindle 70 shown in FIG. 79 are in communication. The polishing liquid sent from the polishing liquid supply source 79 to the spindle 70 is supplied to the polishing pad 76 from the opening at the lower end of the polishing liquid flow path (not shown). The lower surface of the polishing pad 76 in contact with the wafer W is formed with, for example, grid-shaped grooves (not shown). It spreads all over the bottom surface.
The polishing apparatus 1 may be configured to dry-polish the wafer W instead of performing CMP (chemical mechanical polishing) using a polishing liquid.

As shown in FIG. 1, the polishing apparatus 1 includes, for example, control means 9 for controlling the entire apparatus. A control means 9 composed of a CPU or the like is electrically connected to each component of the polishing apparatus 1 . The control means 9 is electrically connected to, for example, the vertical movement means 5 and the polishing means 7, and under the control of the control means 9, the vertical movement means 5 moves the polishing means 7 up and down, and polishing is performed. Rotational movement of the polishing pad 76 in the means 7 and the like are performed.
The polishing apparatus 1 also includes a storage unit 90 configured by a storage element such as a memory.

The control means 9 is connected to the holder load sensor 77 and the table load sensor 38 shown in FIG. 2 via a wired or wireless communication path.
For example, in the holder load sensor 77 and the table load sensor 38, the piezoelectric element constituting the sensor is slightly deformed by the applied load, and a potential difference corresponding to the load is generated in the piezoelectric element. A load detection signal is sent to the control means 9 from the holder load sensor 77 and the table load sensor 38 due to the potential difference generated in the piezoelectric element.

(Embodiment 1 of Wafer Polishing Method: Polishing of Thin Wafer)
Each step of polishing the upper surface Wb of the wafer W using the polishing apparatus 1 shown in FIGS. 1 and 2 will be described below.
When the polishing apparatus 1 actually performs polishing, setup is performed to grasp the relative distance in the Z-axis direction from the holding surface 300a of the holding means 30 to, for example, the lower surface of the polishing pad 76 with high accuracy. As an example of setup, the polishing means 7 is lowered to bring the lower surface of the polishing pad 76 into contact with the holding surface 300a of the holding means 30, and the control means 9 is moved from the polishing feeding position of the polishing means 7 at the time of this contact. The relative distance is grasped and stored in the storage section 90 . Note that setup does not have to be performed.

Further, in the storage unit 90, among the plurality of wafers W having different thicknesses stored in the wafer cassette 21, the thickest thickness (for example, a thickness of 3.5 mm) of the assumed wafer W is stored in advance. It is memorized by memorizing, or by an operator's input via an input means (not shown) (a touch panel or a keyboard attached to the polishing apparatus 1). Then, from the data on the thickness of the thickest wafer W and the data on the relative distance in the Z-axis direction from the holding surface 300a to the lower surface of the polishing pad 76, which is grasped by the setup, the lower surface of the polishing pad 76 shown in FIG. A preparation position Z1 (see FIG. 3) of the polishing pad 76 provided with a predetermined gap from the upper surface Wb of the thickest wafer W held by the holding means 30 is grasped by the control means 9 and stored in the storage section 90. be.
A graph F1 shown in FIG. 3 is a graph showing changes in the height position of the polishing pad 76. As shown in FIG.

At the preparation position Z1, for example, if the thickest wafer W among the plurality of wafers W having different thicknesses stored in the wafer cassette 21 shown in FIG. The position where the bottom surface of the polishing pad 76 is 0.1 mm higher than the height position Z0 (see FIG. 3) of the top surface Wb of the wafer W that is assumed to be the thickest, that is, the height position 3.6 mm above the holding surface 300a is the position where the lower surface of the polishing pad 76 is located.

In addition, in the processing conditions (device data) set in the polishing apparatus 1, the thickness of the wafer W before polishing (input thickness) is, for example, the assumed thickest thickness of 3.5 mm (hereinafter referred to as the assumed thickest thickness ) is set, input to the control means 9 by an operator or the like, and stored in the storage unit 90 .

(1) Preparing Position Positioning Step First, a conveying means (not shown) pulls out one wafer W from the wafer cassette 21 shown in FIG. W is placed on the holding surface 300a with the upper surface Wb facing upward. In this state, the holding means 30 sucks and holds the wafer W on the holding surface 300a by transmitting the suction force generated by the operation of the suction source (not shown) to the holding surface 300a.
In the first embodiment, the wafers W held by the holding means 30 are thinner than the average thickness of the wafers W housed in the wafer cassette 21, for example.

Next, the holding means 30 holding the thin wafer W by suction moves in the Y-axis direction, and the polishing pad 76 of the polishing means 7 and the thin wafer W held by the holding means 30 are aligned. In the alignment in the first embodiment, as shown in FIG. 2, the polishing pad 76 is always in contact with the entire upper surface Wb of the wafer W during the polishing process, and a polishing liquid (not shown) having an opening at the center of the polishing pad 76 is used. The holding means 30 is positioned at a predetermined position so that the channel is blocked by the upper surface Wb of the wafer W. As shown in FIG. In the example shown in FIG. 2, the outer periphery of the polishing pad 76 and the outer periphery of the wafer W are substantially matched, but they do not have to be substantially matched.

Under the control of the control means 9, the vertical movement means 5 moves the polishing means 7, which is positioned at, for example, the origin height position, at a predetermined speed, that is, when polishing is performed by bringing the polishing pad 76 into contact with the wafer W. It descends faster than the speed. Further, the control means 9 constantly grasps the height position of the polishing means 7 which has started to descend from the origin height position.
The lower surface of the polishing pad 76 of the polishing means 7 shown in FIG. 2 is positioned at the preparation position Z1, and a predetermined gap is provided between the upper surface Wb of the thin wafer W and the lower surface of the polishing pad 76. Since the wafer W held is a thin wafer, the size of the gap is larger than 0.1 mm.
As an example of operation control of the vertical movement means 5 by the control means 9, for example, when the motor 52 of the vertical movement means 5 is a servo motor, the rotary encoder of the servo motor also functions as a servo amplifier. It is connected to the control means 9, and after an operation signal is supplied to the servomotor from the output interface of the control means 9, the rotation speed of the servomotor is output to the input interface of the control means 9 as an encoder signal. After receiving the encoder signal, the control means 9 can lower the polishing means 7 at a desired lowering speed by the vertical movement means 5 while sequentially recognizing the height position of the lower surface of the polishing pad 76 .

Further, as the motor 72 shown in FIGS. 1 and 2 rotates the spindle 70, the polishing pad 76 rotates at a predetermined rotational speed.

(2-1) First Lowering Process After positioning the polishing pad 76 at the preparation position Z1 shown in FIGS. The polishing pad 76 is lowered at speed and then stopped. That is, for example, the up-and-down movement means 5 lowers the polishing pad 76 by a preset distance of 50 μm at a lowering speed of 2 mm/sec, which is a preset air cut lowering speed, and then performs step feeding to stop. Note that the preset descending speed of 2 mm/sec is set faster than the air cut descending speed at the time of air cutting (at the time of idle cutting) in the conventional polishing method. Also, the distance and the descending speed are changed to appropriate values depending on the type of polishing pad 76 and the like. Further, the distance is set so that the load value measured by the holder load sensor 77 becomes smaller than a preset threshold value when the polishing pad 76 which is not in contact with the wafer W is lowered and brought into contact with the wafer W. is set. In other words, the distance should be within the crushing margin of the polishing pad 76 .

(3-1) First Judgment Step After the polishing pad 76 is stopped by the lowering step, for example, in the first embodiment, the load values measured by the three holder load sensors 77 shown in FIG. It is determined whether or not the above is satisfied. The determination process may be performed based on the load value measured by the table load sensor 38 instead of the holder load sensor 77 .
For example, the storage unit 90 of the control means 9 stores in advance a threshold value G1N (see FIG. 3) to be compared with the load value measured by the holder load sensor 77 when the wafer W is polished. This threshold value G1N is a value selected experimentally, empirically, or theoretically. This is the load value stored for
A graph F2 shown in FIG. 3 indicates changes in the load value measured by the holder load sensor 77. As shown in FIG.

The threshold value G1N shown in FIG. 3 is, for example, an intermediate value between the upper limit load value G2N and the lower limit load value G3N, which are the predetermined load range. The upper limit load value G2N to the lower limit load value G3N, which are the predetermined load range, are values selected experimentally, empirically, or theoretically, and the polishing pad 76 appropriately polishes the upper surface Wb of the wafer W. This is the range of load values stored in the storage unit 90 for the purpose.

As shown in FIG. 3, in the first load measurement by the holder load sensor 77 in the first determination process, the load value measured by the holder load sensor 77 is not equal to or greater than the threshold value G1N. Therefore, the judgment unit 91 of the control means 9, which compares and monitors the information about the load value sent from the holder load sensor 77 (for example, the load value 0N) and the threshold value G1N, detects the load value measured by the holder load sensor 77. is less than the preset threshold value G1N.
While the load is being measured by the holder load sensor 77, the polishing pad 76 is stopped from descending. in a short time.

(4-1) First Repetition Step Since it was determined in the first determination step that the load value measured by the holder load sensor 77 was less than the threshold value G1N, a repetitive step of repeating the descending step and the determination step was performed. be implemented.

(2-2) n-th lowering step For example, after the lowering step and the judgment step are repeated a plurality of times, the vertical movement means 5 moves the polishing pad 76 by a preset distance of 50 μm at 2 mm/sec. By executing the step feed that lowers and stops, the lower surface of the polishing pad 76 of the polishing means 7 is positioned at the contact height position Z2 shown in FIG.

(3-2) nth Determination Process After the polishing pad 76 is stopped by the nth descent process, it is determined whether or not the load value measured by the holder load sensor 77 is equal to or greater than a preset threshold value G1N.
As shown in FIG. 3, in the n-th load measurement by the holder load sensor 77 in the n-th determination step, the holder load sensor 77 measures a load value G4N equal to or greater than the threshold value G1N. Then, the determination unit 91 of the control means 9, which compares and monitors the information about the load value G4N sent from the holder load sensor 77 and the threshold value G1N, determines whether the measured load value G4N is equal to or greater than the preset threshold value G1N. I judge. Then, the determination unit 91 determines that the polishing pad 76 has come into contact with the upper surface Wb of the wafer W.
As described below, the determination unit 91 determines that the polishing pad 76 is already in contact with the upper surface Wb of the wafer W by lowering the polishing pad 76 by a preset distance. When the load value G4N measured by the holder load sensor 77 becomes equal to or greater than the preset threshold value G1N after performing the lowering step and the determination step from the state where the load value G4N is less than the preset threshold value G1N, polishing is performed. It may be determined that the pad 76 has come into contact with the wafer W. FIG.

(4-2) nth Repetition Process Since it was determined in the nth determination process that the load value measured by the holder load sensor 77 was equal to or greater than the threshold value G1N, the repetitive process of repeating the lowering process and the determination process was not performed. First, a polishing step, which will be described later, is performed. In the n-th determination process, even if all the three holder load sensors 77 do not measure the load G4N equal to or greater than the threshold G1N, at least one holder load sensor 77 measures the load G4N equal to or greater than the threshold G1N. , the polishing step described later may be performed without performing the n-th repetition step.

(5) Polishing process Since it is determined that the load value G4N measured by the holder load sensor 77 is equal to or greater than the threshold value G1N in the n-th determination process, the upper limit load value G2N to the lower limit load value, which is a predetermined load range including the threshold value G1N, The wafer W is polished while the load in G3N is applied to the wafer W.
That is, the polishing means 7 shown in FIG. 2 is lowered by the vertical movement means 5 at a predetermined polishing feed speed, that is, at a speed slower than the air cut descent speed, which is the descent speed from the preparation position Z1 to the contact height position Z2, for example. Then, while the lower surface of the polishing pad 76 is in contact with the upper surface Wb of the wafer W, polishing is performed. Further, during the polishing process, the wafer W held on the holding surface 300a rotates as the holding means 30 rotates at a predetermined rotational speed, and the entire upper surface Wb of the wafer W is polished by the polishing pad 76. be.

During the polishing process, slurry (polishing liquid) is supplied to the contact portion between the wafer W and the polishing pad 76 . That is, a slurry (for example, a polishing liquid containing SiO ₂ , Al ₂ O ₃ or the like as free abrasive grains) is delivered from the polishing liquid supply source 79 shown in FIG. supplied to the contact site with

Further, during the polishing process, under the control of the control means 9, for example, the operation signal supplied to the motor 52 of the vertical movement means 5 is reduced to weaken the pressing of the polishing pad 76 against the wafer W; The operation signal supplied to the motor 52 of the vertical movement means 5 is increased to strengthen the pressing of the polishing pad 76 against the wafer W. The wafer W is polished while applying a load within a predetermined load range including the threshold value G1N from the upper limit load value G2N to the lower limit load value G3N to the wafer W based on the monitoring by the determination unit 91 of the fluctuation of the load value. .
Then, while controlling the polishing time (controlling the amount of polishing), the lower surface of the polishing pad 76 of the polishing means 7 is positioned at the polishing end height position Z3 shown in FIG. The means 5 raises the polishing means 7 and separates it from the wafer W. As shown in FIG.

As described above, in the wafer polishing method according to the present invention, the polishing pad 76 is positioned at the preparation position Z1 in which the gap is provided between the upper surface Wb of the wafer W held by the holding surface 300a and the lower surface of the polishing pad 76. After positioning the polishing pad 76 at the preparation position Z1, the vertical movement means 5 is used to move the polishing pad 76 at a preset distance and speed (for example, a speed higher than the conventional air cut lowering speed). a descending step of descending and stopping; a determining step of determining whether or not the load value measured by the holder load sensor 77 after the polishing pad 76 is stopped by the descending step is equal to or greater than a preset threshold value G1N; A repeating step of repeating the lowering step and the determining step until it is determined that the load value measured by the holder load sensor 77 is equal to or greater than the threshold value G1N, and the determination step is performed until the load value measured by the holder load sensor 77 is equal to or greater than the threshold value G1N. a polishing step of polishing the wafer W while applying a load within a predetermined load range including the threshold value G1N to the upper limit load value G2N to the lower limit load value G3N to the wafer W when it is determined that there is a Even if the thickness of a plurality of wafers W stored in 21 is not uniform, thin wafers W having different thicknesses can be polished. That is, even if the thickness is different, the same air cut is performed and the same polishing load (a load within the upper limit load value G2N to the lower limit load value G3N, which is a predetermined load range including the threshold value G1N) is applied to the wafer W. You will be able to grind and polish. Therefore, it is possible to prevent the time required for the lower surface of the polishing pad 76 to contact the upper surface Wb of the wafer W (air cut time) from becoming longer.

A graph F3 shown in FIG. 4 is a graph showing changes in the height position of the polishing pad 76 in the conventional method of polishing a wafer W (wafer W thinner than the set thickness). The set thickness in the conventional polishing method is, for example, the average thickness of the wafers W housed in the wafer cassette 21 . A graph F4 shown in FIG. 4 is a graph showing changes in the load value measured by the holder load sensor 77 in the conventional polishing method for the wafer W (wafer W thinner than the set thickness). In the conventional method for polishing a wafer W, after the lower surface of the polishing pad 76 of the polishing means 7 is positioned at the air cutting start position Z11, the vertical movement means 5 moves the polishing means 7 without step-feeding. The polishing means 7 is lowered at an air cut descent speed (eg, 5 μm/sec) slower than the cut descent speed (eg, 2 mm/sec). The air cut start position Z11 is, for example, when a wafer W having a set thickness is held by the holding means 30, the lower surface of the polishing pad 76 is a predetermined distance from the contact height position Z4 with respect to the upper surface Wb of the wafer W having a set thickness. (for example, 0.1 mm) is set at a higher position. The time required for the lower surface of the polishing pad 76 to come into contact with the upper surface Wb of the wafer W (air cut time) is longer than in the method of polishing the wafer W according to the present invention, and as shown in FIG. It can be seen that the wafer polishing method according to the present invention can shorten the air-cut time.
For example, when the thickness of the wafer W is 50 μm, the conventional polishing method takes 20 seconds because the wafer W descends at 5 μm/second from 100 μm above the upper surface Wb of the wafer W, which is the air cutting start position Z11. . On the other hand, in the present invention, the air cut time is 0.2 in order to measure the load value each time the air cut time is moved stepwise by 50 μm at 2 mm/sec from 3.6 mm above the holding surface 300a of the holding means 30 . It takes seconds, and the number of steps is performed 71 times, which is about 16 seconds.

A graph F7 shown in FIG. 5 is a graph showing changes in the height position of the polishing pad 76 in the conventional method of polishing a wafer W (wafer W having a set thickness). Graph F8 shown in FIG. 5 is a graph showing changes in the load value measured by the holder load sensor 77 in the conventional method of polishing a wafer W (wafer W having a set thickness). In the conventional method for polishing a wafer W, after the lower surface of the polishing pad 76 of the polishing means 7 is positioned at the air cutting start position Z11, the vertical movement means 5 moves the polishing means 7 without step-feeding. The polishing means 7 is lowered at an air cut descent speed (eg, 5 μm/sec) slower than the cut descent speed (eg, 2 mm/sec). The air cut start position Z11 is such that when a wafer W having a set thickness is held by the holding means 30, the lower surface of the polishing pad 76 is positioned a predetermined distance (for example, 0.1 mm) from the upper surface Wb of the wafer W having a set thickness. ) is set at a higher position. Then, the time (air cut time) until the lower surface of the polishing pad 76 contacts the upper surface Wb of the wafer W becomes longer than in the polishing method of the wafer W according to the present invention.

(Wafer polishing method embodiment 2: Polishing of thick wafer)
Each step of polishing the upper surface Wb of the thick wafer W using the polishing apparatus 1 shown in FIGS. 1 and 2 will be described below.
When the polishing apparatus 1 actually performs polishing, for example, it is set up to grasp the relative distance in the Z-axis direction from the holding surface 300a of the holding means 30 to the lower surface of the polishing pad 76 with high accuracy.

Data on the thickness of the thickest wafer W (thickness 3.5 mm, for example) and data on the relative distance in the Z-axis direction from the holding surface 300a to the lower surface of the polishing pad 76 grasped by setup are shown in FIG. The preparation position Z1 (see FIG. 6) of the polishing pad 76 with a predetermined gap (for example, 0.1 mm) between the lower surface of the polishing pad 76 and the upper surface Wb of the thickest wafer W held by the holding means 30 is , are grasped by the control means 9 and stored in the storage unit 90 .
A graph F9 shown in FIG. 6 is a graph showing changes in the height position of the polishing pad 76. As shown in FIG.

(1) Preparing Position Positioning Process First, a conveying means (not shown) pulls out one wafer W from the wafer cassette 21 shown in FIG. Then, the holding means 30 sucks and holds the wafer W on the holding surface 300a. In the third embodiment, the wafers W held by the holding means 30 are, for example, wafers W that are thicker than the average thickness of the wafers W housed in the wafer cassette 21 .
Next, the holding means 30 sucking and holding the thick wafer W moves in the Y-axis direction, and the polishing pad 76 of the polishing means 7 and the thick wafer W held by the holding means 30 are aligned as in the first embodiment. is done in the same way as

Under the control of the control means 9, the vertical movement means 5 moves the polishing means 7 positioned at the origin height position, for example, at a predetermined speed, that is, when the polishing pad 76 is brought into contact with the wafer W for polishing. It descends at a higher speed than the descending speed. Further, the height position of the polishing means 7 that has started to descend is always grasped by the control means 9 . The lower surface of the polishing pad 76 of the polishing means 7 shown in FIGS. 2 and 6 is positioned at the preparation position Z1, and a predetermined gap is provided between the upper surface Wb of the thick wafer W and the lower surface of the polishing pad 76. FIG. The size of the gap is 0.1 mm.
Further, as the motor 72 shown in FIG. 1 rotates the spindle 70, the polishing pad 76 rotates at a predetermined rotation speed.

(2-1) First Lowering Step After positioning the polishing pad 76 at the preparation position Z1 shown in FIGS. A step feed is executed to lower the polishing pad 76 by 50 μm at a preset air cut lowering speed of 2 mm/sec and then stop. The preset descending speed of 2 mm/sec is set faster than the air cut descending speed during air cutting in the conventional polishing method.

(3-1) First Judgment Step After the polishing pad 76 is stopped by the lowering step, for example, it is judged whether or not the load values measured by the three holder load sensors 77 are equal to or greater than a preset threshold value.
The threshold value G1N shown in FIG. 6 and stored in the storage unit 90 of the control means 9 is, for example, an intermediate value between the upper limit load value G2N and the lower limit load value G3N, which are the predetermined load range. In the first load measurement by the holder load sensor 77 in the first determination process, the load value measured by the holder load sensor 77 is not equal to or greater than the threshold value G1N. The determination unit 91 of the control means 9, which compares and monitors the information (for example, the load value 0N) and the threshold value G1N, determines that the load value measured by the holder load sensor 77 is less than the preset threshold value G1N.
A graph F10 shown in FIG. 6 indicates changes in the load value measured by the holder load sensor 77. As shown in FIG. Further, while the load is being measured by the holder load sensor 77, the downward movement of the polishing pad 76 is temporarily stopped.

(4-1) First Repetition Process Since it was determined in the first determination process that the load value measured by the holder load sensor 77 was less than the threshold value G1N, a repetitive process of repeating the lowering process and the determination process is performed. be.

(2-2) n-th lowering step For example, after the lowering step and the judgment step are repeated a plurality of times, the vertical movement means 5 grinds at 2 mm/sec for a preset distance of 50 μm. By carrying out the step feed that lowers and stops the pad 76, the lower surface of the polishing pad 76 of the polishing means 7 is positioned at the contact height position Z6 of the thick wafer W shown in FIG.

(3-2) nth Determination Process After the polishing pad 76 is stopped by the nth descent process, it is determined whether or not the load value measured by the holder load sensor 77 is equal to or greater than a preset threshold value G1N. As shown in FIG. 6, in the n-th load measurement by the holder load sensor 77 in the n-th determination step, the holder load sensor 77 measures a load value G4N equal to or greater than the threshold value G1N. Then, the determination unit 91 of the control means 9, which compares and monitors the information about the load value G4N sent from the holder load sensor 77 and the threshold value G1N, determines whether the measured load value G4N is equal to or greater than the preset threshold value G1N. It is determined that the polishing pad 76 has come into contact with the upper surface Wb of the wafer W. As described below, the determination unit 91 determines that the polishing pad 76 is already in contact with the upper surface Wb of the wafer W by lowering the polishing pad 76 by a preset distance. When the load value G4N measured by the holder load sensor 77 becomes equal to or greater than the preset threshold value G1N after performing the lowering step and the determination step from the state where the load value G4N is less than the preset threshold value G1N, polishing is performed. It may be determined that the pad 76 has come into contact with the wafer W. FIG.

(4-2) n-th Repetition Process Since it is determined in the n-th determination process that the load value measured by the holder load sensor 77 is equal to or greater than the threshold value G1N, the later-described polishing process is performed.

(5) Polishing process Since it is determined that the load value G4N measured by the holder load sensor 77 is equal to or greater than the threshold value G1N in the n-th determination process, the upper limit load value G2N to the lower limit load value, which is a predetermined load range including the threshold value G1N, The wafer W is polished while the load in G3N is applied to the wafer W.
That is, the polishing means 7 is lowered at a predetermined polishing feed rate by the vertical movement means 5, and the lower surface of the polishing pad 76 is brought into contact with the upper surface Wb of the wafer W, thereby performing the polishing process. Also, as the holding means 30 rotates, slurry is supplied from the polishing liquid supply source 79 to the contact portion between the wafer W and the polishing pad 76 .

During the polishing process, the control means 9 controls the vertical movement means 5 to apply a load within a predetermined load range including the threshold value G1N to the wafer W from the upper limit load value G2N to the lower limit load value G3N. is being polished.
Then, while the polishing time is controlled, the lower surface of the polishing pad 76 of the polishing means 7 is positioned at the polishing end height position Z7 shown in FIG. is raised and separated from the wafer W.

As described above, in the wafer polishing method according to the present invention, the polishing pad 76 is positioned at the preparation position Z1 in which the gap is provided between the upper surface Wb of the wafer W held by the holding surface 300a and the lower surface of the polishing pad 76. After positioning the polishing pad 76 at the preparation position Z1, the vertical movement means 5 is used to lower the polishing pad 76 at a preset distance and speed (faster than the conventional air cut lowering speed). a descending step of stopping the polishing pad 76 by the descending step, a determining step of determining whether or not the load value measured by the holder load sensor 77 is equal to or greater than a preset threshold value G1N after the polishing pad 76 is stopped by the descending step; A repeating step of repeating the lowering step and the determining step until it is determined that the load value measured by the sensor 77 is equal to or greater than the threshold value G1N, and the determining step determines that the load value measured by the holder load sensor 77 is equal to or greater than the threshold value G1N. and a polishing step of polishing the wafer W while applying a load within a predetermined load range from the upper limit load value G2N to the lower limit load value G3N including the threshold value G1N to the wafer W. Even if the thickness of a plurality of stored wafers W is not uniform, the thick wafers W can be polished while applying a load within a predetermined load range including the threshold value G1N from the upper limit load value G2N to the lower limit load value G3N. In addition, since the polishing pad 76, which descends at high speed before starting air cutting, does not contact the upper surface Wb of the thick wafer W at high speed, the wafer W exceeds the allowable value (upper limit load value G2N (above)) to prevent cracking.

A graph F11 shown in FIG. 7 is a graph showing changes in the height position of the polishing pad 76 in the conventional method of polishing a wafer W (wafer W thicker than the set thickness). The conventional set thickness is, for example, the average thickness of the wafers W housed in the wafer cassette 21 . A graph F12 shown in FIG. 8 is a graph showing changes in the load value measured by the holder load sensor 77 in the conventional polishing method for the wafer W (wafer W thicker than the set thickness). In the conventional method for polishing a wafer W, after the lower surface of the polishing pad 76 of the polishing means 7 is positioned at the air cutting start position Z11, the vertical movement means 5 moves the polishing means 7 without step-feeding. The polishing means 7 is lowered at an air cut descent speed (eg, 5 μm/sec) slower than the cut descent speed (eg, 2 mm/sec). However, in the preceding stage, the air cutting start position Z11 is such that, for example, when a wafer W having a set thickness is held by the holding means 30, the lower surface of the polishing pad 76 is a predetermined distance ( For example, 0.1 mm), if the wafer W held by the holding means 30 is thicker than the set thickness, the wafer W is brought into contact with the air cutting start position Z11. The polishing pad 76 lowered at a higher speed than the lowering speed during polishing contacts the upper surface Wb of the wafer W, which is thicker than the set thickness, at a high speed, and the wafer W is increased to the allowable value or more (the upper limit load value G2N or more). It may crack under load.

The method of polishing a wafer according to the present invention is not limited to this embodiment, nor is the configuration of the polishing apparatus 1 shown in the accompanying drawings limited to this, and the effects of the present invention are exhibited. It can be changed as appropriate within a possible range.

W: wafer Wa: lower surface of wafer Wb: upper surface of wafer 1: polishing apparatus 10: apparatus base 11: column 21: wafer cassette 215: shelf 30: holding means 300a: holding surface 39: cover 34: Y-axis moving means 340 : Ball screw 342: Motor 343: Movable plate 36: Tilt adjusting means 33: Table base 38: Table load sensor 5: Vertical movement means 50: Ball screw 52: Motor 53: Elevating plate 7: Grinding means 70: Spindle 71: Housing 72: Motor 73: Mount 76: Polishing pad 75: Holder 75b: Bottom plate 75c: Side plate 77: Holder load sensor 773: Fixing bolt 9: Control means 90: Storage unit 91: Judging unit

Claims (1)

holding means for holding the wafer on the holding surface; polishing means for polishing the wafer by bringing the lower surface of the polishing pad into contact with the upper surface of the wafer held by the holding means; A wafer polishing method using a polishing apparatus provided with a vertical movement means for moving and a load sensor for measuring the load of pressing the polishing pad against the wafer held on the holding surface, the method comprising:
a preparation position positioning step of positioning the polishing pad at a preparation position in which a gap is provided between the upper surface of the wafer held by the holding surface and the lower surface of the polishing pad;
a descending step of, after positioning the polishing pad at the preparation position, descending the polishing pad at a preset distance and speed using the vertical movement means and then stopping;
a determination step of determining whether or not the load value measured by the load sensor is equal to or greater than a preset threshold after the polishing pad is stopped by the descending step;
a repeating step of repeating the descending step and the determining step until the determining step determines that the load value measured by the load sensor is equal to or greater than the threshold value;
a polishing step of polishing the wafer while applying a load within a predetermined load range including the threshold value to the wafer when the determination step determines that the load value measured by the load sensor is equal to or greater than the threshold value; A method for polishing a provided wafer.

Images